In the field of hydraulic cylinders, a variety of systems have been proposed in which the displacement of the elements of the cylinder is electrically sensed and displayed or used to perform control functions. Conventional transducers have serious deficiencies owing in part to difficulties in mounting the units and the harsh environmental conditions to which they are exposed. Transducers used on hydraulic systems in the heavy equipment industry are particularly subject to damage from the severe work environment. Hydraulic cylinders are typically located in relatively unprotected areas and subjected to, for example, high g-forces, wide temperature variations, dust, water, debris, etc. which can result in both electrical and mechanical failure of the sensor.
Ideally, the transducer should be isolated from the work environment. One method for effecting such isolation is by mounting the transducer internal the cylinder, as illustrated in U.S. Pat. No. 3,726,191 issued to Johnston et al. Johnston employs a resistive strip positioned in the cylinder and fixed relative to the piston. A variable position tap is fixedly attached to the piston rod and slidably engagable with the resistive strip. While Johnston has developed a transducer which is less likely to be damaged by the work environment, a wear element has been introduced which has an accuracy that degrades over time and must be periodically replaced. Further, Johnston's sensor requires a customized hydraulic cylinder configuration and expensive retooling necessary to produce the new cylinder. Retrofitting existing hydraulic cylinders with the Johnston sensor is a difficult and costly operation.
The present invention is directed to overcoming one or more of the problems as set forth above.